LCD (Liquid Crystal Display) is extensively used nowadays, and various backlight modules are also developed to illuminate LCD. The lamps of a backlight module are also continuously increased to provide sufficient illumination for the persistently-increasing size LCD. Thus, there are many types of multi-lamp backlight modules and multi-lamp driving systems developed. A R.O.C. patent No. I243629 disclosed a “Multi-Lamp Driving System”, which uses a plurality of AC voltage sources and a multi-phase transformer having a plurality of different-phase coil windings to drive a plurality of loads, wherein the currents passing through the loads have an identical value. As shown in FIG. 11, FIG. 15 and FIG. 16 of the prior art patent, lamps are cascaded to form a loop, and several loops can be further connected in parallel to obtain various lamp arrangements. However, this prior art lacks a protection measure for an open loop or a broken lamp. Once one of the lamps is broken or dropped, the driving system will have an imbalanced power distribution, which will result in abnormal current and brightness in some lamps. The lamps having too high a current may deteriorate in advance and consume too much power. Therefore, it is desirous to have a detection/protection mechanism to detect dropped or broken lamps and prevent from imbalanced power distribution.